Method and means for regulating temperature in ore roasting furnaces



May 28, 1940- D. 1.. CRAMP 2,202,245 METHOD AND MEANS FOR REGULATING TEMPERATURE IN ORE ROASTING FURNACES Filed July 15, 1959 Patented May 28, 1940 UNITED "STATES PATENT OFFlCE r METHOD AND MEANS FoR REGULATING TEMPERATURE 1 oRE ROASTING F R- NACES David Leo Cramp, Kirkland Lake, Ontario, Canada, assignor to Lake Shore Mines, Limited, Kirkland Lake, Ontario, Canada Application July 15, 1939, Serial No. 284,586

5. Claims. This invention relates to a method and means for air-cooling parts of an ore roasting furnace of the single hearth type and for therebyregulating the temperature within the furnace.

While it has previously been proposed to em-- ploy air in combination. with water for cooling the rabble arms in a single hearth furnace of, for instance, the Edwards type, it has not previously been suggested, so far as applicant is aware, to employ air exclusively for the cooling of rabble arms and other parts of such single hearth furnaces. Moreover, it has'not previously been proposed to use air cooling means for such furnace parts for the purpose of regulating the temperature of the charge within the furnace. It will be recognized that the use of water cooling arrangements for regulating the inner temperature of the furnace is impractical since, in order to maintain a water circulation, the temperature thereof must be kept below "boiling.

Thus the temperature of the parts in contact with the water will be maintained below a certain maximum degree, which is too low to be of utility in regulating the roast temperature in the furnace.

The object of the invention is to provide a method and means for air cooling parts of a single hearth roasting furnace, including the rabble arms, hearth and arch, and for regulating the temperature of the roast within the furnace by means of the air cooling means.

The invention will be described with reference to the accompanying drawing inwhich Figure 1 is a sectional elevation of a single hearth furnace to which is applied an air cooling means in accordance with the invention,

Figure 2 is an enlarged plan of an air circulation fitting for the rabble arm shaft, and

Figure 3 is an enlarged sectional elevation of the fitting illustrated in Figure 2.

In the drawing, I is an ore roasting furnace having a single hearth 2 composed of hollow tiles 3 and a metal arch 4 in which are formed a plurality of interconnected ducts 5. Rotatably mounted on the frame 6 of the furnace are rabbles 1 having vertical spindle shafts 8 on the lower end of which within the furnace are arms 9. Each shaft and arm are hollow, an inner partition II] being provided and extending from adjacent the end of the arm to a point just above the arch. Thus, air admitted to the hollow shaft may circulate down one side of the shaft and arm within the furnace and up the other side of the shaft and arm, an outlet II being provided therefor outside the furnace. An air outlet plug I I for admitting combustion air within the furnace may also be provided.

Each shaft 8 is rotated by means of a bevel gear I2 having a bearing I2 fixed to the top of the shaft and bevel pinion I3 meshing with gear l2 and fixed to a horizontal driving shaft I4.

Air is supplied to the hollow within each shaft 8 through a cylindrical two-part fitting I5 having an annular downwardly projecting seat I6 bearing upon an annular depressed seat I 6 on the top of bearing I2. The fitting I5 is of a weight that its seat I5 provides a substantially air tight seal with the bearing l2. The fitting. I5 is provided with an air duct I'I leading from its side surface to the hollow within the shaft 8. The duct II hasa nipple l8 at the surface of the fitting whereby an air hose connection I9 may be attached thereto; The hose connection is also attached to a nipple 20 in an air header 2| served by a, pipe 2| leading from a housing 22 within- Which is mounted a fan 23.

The fitting I5 is provided on its upper surface with a groove 24 adapted to accommodate pas- I sage therethrough of the horizontal shaft Hi. The shaft I l thus serves to maintain the fitting in its position on top of the bearing I2.

An air pipe 25 leads from the fan housing 22 to a header 25' adjacent the hearth Zand an air connection 26 leads therefrom to the hollow within the hearth'at one end thereof. The other end of the hearth may be open to the atmosphere to provide an air outlet.

Another air pipe 21 leads from pipe 25 and is provided with branches 28 and 29 leading to headers 28' and 29' adjacent either end of the. arch 4. Air connections 30 and 3| connect the respective branches to ducts 5. Air outlets 32, for discharging air outside the furnace, and outlet plugs 33, for discharging air, as required, within the furnace, are provided in the arch.

Draft gauges 34 whereby the air pressure may be controlled are provided.

Dampers 35 for controlling theair flow are provided in pipes 2|, 25, 28 and 29.

In operating the furnace in accordance with the invention, while roasting a charge of sulphide ore concentrate, a volume of air is circulated through the rabbles and, if required, through the arch, to maintain a predetermined temperature within the furnace. -'I'he roasting temperature of sulphide ores is approximately 1050 R, such temperature being'taken at a point above the charge and at a central'portion of the furnace. This temperature must be maintained for an effective roast. The. normal temperature of a roasting charge, if not controlled, will vary greatly and substantially in accordance with the sul-- phur content of the ore concentrate forming the charge. Thus, a concentrate containing 25% and upwards of sulphur is usually regarded as a self-roasting concentrate, the sulphur content providing the necessary fuel for roasting the ore. As the percentage of sulphur content rises, the additional fuel thus provided increases the temperature of the charge unless means are provided to control the same. As the percentage of sulphur content decreases, the temperature of the charge also decreases unless additional fuel is provided. A concentrate containing below 25% sulphur is not usually regarded as self-roasting when water-cooled rabbles are employed since the rabbles must be maintained at so low a temperature for circulation purposes that the combustion ceases.

In accordance with the invention, the temperature of the charge, which, as previously set forth, is substantially dependent on the sulphur content of the charge, is taken at a suitable point in the furnace, which point is usually above the roasting charge and centrally of the furnace. Such temperature is then raised or lowered by decreasing or increasing the volume of air circulated through the rabbles and, if necessary, the arch, whereby the correct roasting temperature of approximately 1050 F. is maintained.

The present invention permits the self-roasting of ore concentrates containing as low as 19% sulphur since a much higher temperature of rabbles than that possible with water-cooling may be maintained by decreasing the volume of circulatlng air while yet providing sumcient cooling air to prevent burning of the rabble arms.

In the roasting of concentrates containing such a low sulphur content, it may not be necessary to circulate cooling air through the arch, either for the purpose of controlling the furnace temperature or of preventing injury to the arch itself.

When a charge containing a high percentage of sulphur is being roasted and the furnace temperature tends normally to increase, a greater volume of air is circulated through the rabbles and the arch to maintain a lower temperature.

The provision of a cooling air circulation in the arch, in addition to serving to control the furnace temperature, is also advantageous from a maintenance standpoint since possible injury to the arch and supporting structure from overheating is greatly lessened thereby.

The air cooling of the hearth is important in that it makes it possible to reduce the temperature of the roasted charge quickly. If no attempt is made to hasten the cooling rate of the roasted charge, a long distance of travel for the charge through a cooling zone is necessary to permit a sufficient drop in the temperature of the charge. Thus, the overall length of the furnace is lessened by the omission of a special cooling zone, and the initial cost of installation of the furnace decreased accordingly.

I claim:

1. In the roasting of sulphide ores in a single hearth furnace, the method of regulating the furnace temperature comprising circulating air through the' rabble arms and arch of the furnace, and regulating the volume of air so circulated to maintain a predetermined temperature inside the furnace.

2. In an ore roasting furnace having a single hearth, a hollow metal arch and rabble arms therein, means for circulating cooling air through said arch and rabble arms and means for regulating the volume of air so circulated.

3. An ore roasting furnace comprising a single hollow tile hearth, a hollow metal arch, hollow rabble arms within the furnace, means for circulating cooling air through said hearth, arch and rabble arms, and means for regulating the volume of air so circulated.

4. In an ore roasting furnace having a single hearth and a rotatable vertically mounted hollow shaft carrying a hollow rabble arm, means for circulating cooling air through said shaft and rabble armv including a stationary fitting surmounting said shaft and having an air channel therein communicating with the hollow in the shaft, said fitting having a seat adjacent the top of the shaft and being of sufficient weight to maintain an air-tight engagement with said seat.

5. In an ore roasting furnace having a single hearth, a vertically mounted hollow shaft carrying a hollow rabble arm, a gear having a bearing fixed to the top of the shaft and a horizontal driving shaft having a gear adapted to rotate said first gear and vertical shaft, means for circulating cooling air through the vertical shaft and rabble arm including a substantially cylindrical stationary fitting surmounting the vertical shaft and having an air channel therein communicating with the hollow in the shaft, said fitting also having a groove in its upper face through which said horizontal shaft extends and a seat on its lower face engaging said gear bearmg.

D. L. CRLAMP. 

